Evaluation of the Shear Force Behaviour of Composite Slabs

The use of composite slabs is common in the international area and is generally used in office and industrial buildings. Especially the advantages in weight support the use of the composite slab in case of refurbishment. The demand of sustainable solutions promotes the exploration of lightweight composite slabs by substitution of the normal weight concrete by concrete with a dry density between 1,400 kg/dm³ and 1600 kg/dm³. First tests have shown an unexpected failure mode due to the specific properties of lightweight aggregate concrete and its combination with composite sheets. In bending tests of composite slabs with lightweight aggregate concrete (LWAC), the failure was initiated by inclined bending cracks with a vertical offset of the crack surfaces and local buckling of the web of the composite sheet in the decisive crack. The known failure mode of specimens with normal weight concrete (NWAC) could not be validated in these tests. By an examination using the European regulations for the dimensioning of shear loaded concrete beams, a safety deficit about 20 % could be detected. Against this background at the University of Kaiserslautern, a new approach was developed to allow a safe determination of the shear capacity. The concept is comparable to different types of concrete and will be shown in this paper.